Re: [PATCH v15 00/12] tracing: wprobe: x86: Add wprobe for watchpoint

[Jinchao Wang]

On 9/12/2026 9:36 PM, Masami Hiramatsu (Google) wrote:
> On Fri, 11 Sep 2026 15:27:41 +0800
> Jinchao Wang <wangjinchao600@xxxxxxxxx> wrote:
> 
>> Hi Masami,
>>
>> I see the watch address update currently goes irq_work -> workqueue ->
>> on_each_cpu().  I would like to discuss that path.
>>
>> The race window wprobe may be used to watch can be very narrow --
>> sometimes it lives entirely inside a single function -- and the trigger
>> does not always run in in_task() context.  The current path defers the
>> update to a work item, so by the time the debug registers are updated the
>> window may already be gone.
>>
>> Now that we have modify_local_hw_breakpoint_addr(), the trigger could arm
>> the local CPU directly and use smp_call_function_single_async() for the
>> remote ones.  That should improve the overlap between the watch and the window.
> 
> Hm, that is a good idea. Maybe we can check the current context and if
> possible call modify_local_hw_breakcpoint_addr() directly for current
> CPU core, and kick irq_work for other cores.
> Does this make sense for you?

Yes, that makes sense.

> 
> Thanks,
> 
>>
>> What do you think?
>>
>> Thanks,
>> Jinchao
> 
>